Such a device is known from U.S. Pat. No. 3,943,898. In this known device, the reference mark resets a counter which counts pulses produced by a pulse generator at 1.degree. intervals of rotation of the crankshaft of the internal combustion engine. The control signals are produced by a decoder connected to the output of the counter. The control signals are processed by a computer which produces trigger signals for triggering ignition sparks, the number of control signals being equal to the number of engine cylinders. The computer delays the trigger signals with respect to the control signals in accordance with engine operating parameters (engine speed, air intake pressure, cooling water temperature) in order to obtain the desired optimum ignition timing.
The European patent application EP-A 187,182 describes a "High resolution electronic ignition control loop circuit 22 including a voltage-controlled oscillator (VCO) and a digital phase comparator 24, which receives an input signal from a speed sensor together with a divided output signal from the VCO. A filter 26 lies between the phase comparator and the VCO. The speed is sensed from a wheel having a plurality of teeth. Therefore, the response time of the phase lock loop circuit 22 with its filter 26 does not create any problems, when one turn of the sensed wheel is monitored. However, the known circuitry is too slow in its response time, when reference marks are sensed.
An example of a voltage-controlled oscillator is disclosed in "Handbook of Operational Amplifier Circuit Design": McGraw-Hill, 1976, pages 21-5 to 21-10.
Such a device has the disadvantage that, due to its complexity and the large numbers of input parameters required, it does not lend itself to use as a stand-by or back-up system for carrying on the function of a control apparatus in the event of failure of a microprocessor in the latter.